A multistage vehicle automatic transmission is known that includes multiple engagement elements having an engagement state switched by an oil pressure so as to selectively establish a plurality of shift stages based on a combination of engagement and release of the multiple engagement elements corresponding to an oil pressure supplied from a hydraulic circuit. Although clutches and brakes including wet friction materials have been widely used as the engagement elements in such an automatic transmission, these friction materials have been considered to have a problem of a loss due to drag occurring when these friction materials are not engaged. Therefore, an automatic transmission has been proposed that uses a meshing engagement element, i.e., a so-called dog clutch (meshing clutch) as a substitute for a wet friction material. For example, this corresponds to an automatic transmission depicted in Patent Document 1.